FIG. 2 shows a mechanism deck 2 already known for use in such disk recording or playback devices. The deck 2 comprises a chassis 4 formed with an opening 40, two guide rods 41, 41 extending across the opening 40, and a turntable 31 provided at an end portion of the opening 40 for rotating a disk. Mounted on the two guide rods 41, 41 is a pickup 3 having an object lens 30 and movable toward the turntable 31. The pickup 3 is driven by a motor (not shown) on the chassis 4. Provided inside the opening 40 close to the turntable 31 is a sensor switch SW for detecting the pickup 3 as brought closest to the inner periphery of the disk.
The disk 6 is housed in a cartridge 60, which is provided with a movable shutter 61. With the cartridge 60 placed on support pins 42 on the chassis 4, the shutter 61 slidingly moves to expose the lower surface of the disk 6, whereupon a beam is projected from the lens 30 of the pickup 3 for recording or playback.
With reference to FIG. 3, the disk 6 is 64 mm in outside diameter and 29 mm in inside diameter. An inner peripheral region ranging from 29 mm to 32 mm in diameter is referred to as a lead-in area A, a region ranging from 32 mm to 61 mm in diameter as a program area B, and an outer peripheral region ranging from 61 mm to 64 mm in diameter as a lead-out area. Recorded in the lead-in area A is a so-called TOC (table of contents) which is a summary of the information recorded on the disk. For the recognition of the position of the pickup 3, the lead-in area A invariably needs to have recorded therein signals. The program area B has recorded therein desired information such as music signals. Detection of the lead-out area C by the pickup 3 indicates that the pickup 3 has moved out of the program area B.
The pickup 3 is designed to be positioned in the lead-in area A when in a standby state for recording or playback, pressing the sensor switch SW. This position will be referred to as an initial position. The pickup 3 reads the TOC data, recognizes the initial position and thereafter moves to a desired address for recording or playback. For accurate reading of signals from the disk, it is necessary to activate a focus servo for focusing the beam on the disk, a tracking servo for accurately tracking record grooves in the disk and a speed servo for rotating the disk at a constant speed based on the synchronization signal recorded on the disk.
If no signal is recorded at the location first exposed to the beam from the pickup 3, the synchronization signal is undetectable, so that it is impossible to activate the speed servo, consequently failing to effect a proper recording or playback operation subsequently.
Thus, the pickup 3 in the initial position needs to be positioned correctly in the lead-in area.
However, mass production of devices of the type described involves variations in the position or angle of the sensor switch SW mounted on the chassis 4, therefore entailing the likelihood that the pickup 3 will not be positioned correctly in the lead-in area when halted on pressing the sensor switch SW. It is also likely that the pickup 3, which is driven by a motor (not shown), will not be located in the lead-in area when in the initial position even if the sensor switch SW is correctly installed in place owing to variations in the drive force of the motor or to variations in the moving load of the pickup 3. This problem may be overcome by checking every mechanism deck 2 for the installed position of the sensor switch SW, whereas the procedure requires time and labor.